Fix #830, remove incorrect restriction on recursive CTE

src/backend/query_builder.rs

@@ -777,15 +777,6 @@ pub trait QueryBuilder:
             "Cannot build a with query that has no common table expression!"
         );
 
-        if with_clause.recursive {
-            assert_eq!(
-                with_clause.cte_expressions.len(),
-                1,
-                "Cannot build a recursive query with more than one common table! \
-                A recursive with query must have a single cte inside it that has a union query of \
-                two queries!"
-            );
-        }
         for cte in &with_clause.cte_expressions {
             if !cte_first {
                 write!(sql, ", ").unwrap();

tests/sqlite/query.rs

@@ -1792,3 +1792,47 @@ fn sub_query_with_fn() {
         r#"SELECT ARRAY((SELECT * FROM "character"))"#
     );
 }
+
+#[test]
+fn recursive_with_multiple_ctes() {
+    let sub_select1 = Query::select()
+        .column(Asterisk)
+        .from(Char::Table)
+        .to_owned();
+    let sub_select1_name = SeaRc::new(Alias::new("sub1"));
+    let mut sub_select1_cte = CommonTableExpression::new();
+    sub_select1_cte.table_name(sub_select1_name.clone());
+    sub_select1_cte.column(SeaRc::new(Alias::new("a")));
+    sub_select1_cte.query(sub_select1);
+    let sub_select2 = Query::select()
+        .column(Asterisk)
+        .from(Char::Table)
+        .to_owned();
+    let sub_select2_name = SeaRc::new(Alias::new("sub2"));
+    let mut sub_select2_cte = CommonTableExpression::new();
+    sub_select2_cte.table_name(sub_select2_name.clone());
+    sub_select2_cte.column(SeaRc::new(Alias::new("b")));
+    sub_select2_cte.query(sub_select2);
+
+    let mut with = WithClause::new();
+    with.recursive(true)
+        .cte(sub_select1_cte)
+        .cte(sub_select2_cte);
+
+    let mut main_sel2 = Query::select();
+    main_sel2
+        .expr(Expr::col(Asterisk))
+        .from(TableRef::Table(sub_select2_name));
+    let mut main_sel1 = Query::select();
+    main_sel1
+        .expr(Expr::col(Asterisk))
+        .from(TableRef::Table(sub_select1_name))
+        .union(UnionType::All, main_sel2);
+
+    let query = with.query(main_sel1);
+
+    assert_eq!(
+        query.to_string(SqliteQueryBuilder),
+        r#"WITH RECURSIVE "sub1" ("a") AS (SELECT * FROM "character") , "sub2" ("b") AS (SELECT * FROM "character") SELECT * FROM "sub1" UNION ALL SELECT * FROM "sub2""#
+    );
+}